The invention is directed to a method for generating steam, particularly for a cooking device, whereby a liquid within a steam generating vessel is caused to boil by a method of heating at least one heatable wall surface of the steam generating vessel, placing the liquid into rotation while being heated and pressing the liquid against the heatable wall surface due to centrifugal forces due to the rotation, allowing the steam arising due to a vaporization of at least a part of the liquid to escape from the steam generating vessel through a steam outlet and separating drops of the liquid entrained with the steam from the steam. The invention is also directed to an apparatus for generating steam, particularly for a cooking device, which apparatus comprises a steam generating vessel that can be at least partially filled with a liquid via an admission or inlet and from which steam can proceed to a steam outlet, and has a heating device for heating the liquid in the steam generating vessel for the purpose of generating steam.
Traditional steam generators as particularly employed in cooking devices usually comprise a boiler that is partially filled with water that is brought to a boil with heating elements. The space requirement of such a steam generator is mainly defined by two factors, which are the volume part that is filled with liquid water and the volume part of the gas space located above the water.
The first volume part is thereby limited by the size of the heating elements and the space required between the heating elements for the flooding thereof and for carrying off the steam bubbles. The size of the heating elements for a prescribed heating capacity is in turn defined by the Leidenfrost effect, in accord wherewith a specific surface power density of a heating element dare not be exceeded when heating a vaporizable liquid since a closed intermediate steam layer that impedes the heat emission otherwise forms between the surface of the heating element and the liquid. The Leidenfrost effect is nicely demonstrated in the phenomenon that drops of water do not immediately vaporize on a red-hot plate but first move in a quasi dancing motion since, carried by a steam layer that is formed, they move irregularly on the plate.
The second volume part is required in order to separate the steam from entrained drops of water. The size and design of the second volume part, i.e. of the gas space above the liquid, are critical for the quality of the steam. The steam quality is particularly determined by the size of the water surface that the stream of steam must pass. The emerging steam, namely, entrains all the more water the larger the stream of steam is per water surface.
Given traditional steam generators, thus, a high space requirements derives overall from the above considerations when a high steam quality is to be produced. Additionally, however, it must also be pointed out that the time required to make a known, water-filled steam generator operational is also dependent on the amount of water filled in that is required for reliably covering the heating elements, and this, in turn, makes demands of the size of the steam generator.
Steam generators wherein a rotational flow is induced in a steam-generating liquid by injecting a further liquid are known in the field of power plants, particularly nuclear power plants. The centrifugal forces accompanying the rotational flow are thereby used for the precipitation of contaminants, as disclosed by U.S. Pat No. 4,972,804 or, respectively, DE 690 13 906 T2.
Steam generators are also known wherein the entire tubular or barrel-shaped steam generator vessel is placed into rotation. This involves high energy and cost outlays and requires a great structural complexity that makes a rotating bearing of the steam generating vessel necessary, whereby an admission or, respectively, discharge of liquid is necessarily only practical via the axis of rotation. DE 2 214 566, for example, discloses such a rotating steam generator that is designed for the vaporization of organic drive fluids in a closed circulation of a Rankine motor. The steam generator disclosed by German Letters Patent 904 653 works similarly and this, however, additionally comprises a regulation for the supply of liquid for the purpose of creating a liquid ring having a specific thickness.
DE 27 57 913 A1 discloses a rotating steam generator with a rotatably seated boiler that structurally foregoes rotatable lead-throughs for the introduction or, respectively, removal of a liquid work medium.
DE 37 83 361 T2 discloses a tandem separator for a steam/water mixture, whereby helically coiled baffles place the steam/water mixture into rotation.
DE 692 07 830 T2 discloses a steam generator arrangement for ovens wherein thin water jets or, respectively, small drops of water, which are placed into rotation, descend onto a heating device in order to be vaporized.
The known steam generators, however, do not work satisfactorily for the vaporization of tap water but exhibit the serious disadvantage that the dissolved minerals which are contained in the tap water, particularly lime, will deposit at the walls and built-in parts of the steam generator. This can lead to the outage of or damage to the steam generator, which can usually only be prevented by a regular chemical decalcification. The post-operation maintenance jobs that become necessary as a result thereof are in turn cost-intensive.